Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019
Numerator:
Net income attributable to Acadia Healthcare Company, Inc.	$ 33,463	$ (11,254)	$ 42,566	$ 48,140	$ 29,471
Denominator:
Weighted average shares outstanding for basic earnings per share	87,765				87,505
Effect of dilutive instruments	206				189
Shares used in computing diluted earnings per common share	87,971				87,694
Earnings per share attributable to Acadia Healthcare Company, Inc. stockholders:
Basic	$ 0.38				$ 0.34
Diluted	$ 0.38				$ 0.34